Comparisons of atomic thermal motions for graphite at 300 K based on X-ray, neutron, and phonon-spectrum data

The mean-square amplitudes of vibration in graphite based on an X-ray charge-density analysis are 0.0032 (2) and 0.0140 (3) Ų parallel to and perpendicular to the basal plane, respectively. Values for the parallel vibrations of 0.0031 (6) and 0.0032 Ų were derived from temperature-dependent neutron measurements and a calculated phonon spectrum. The neutron measurements and the phonon spectrum both predict lower values [0.0090 (20) and 0.0098 Ų] for the out-of-plane vibrations. This small discrepancy may be caused by small changes in the core atomic scattering factors from the free-atom values or by a deficiency in the phonon-spectrum model.